Second q-shifted factorial
From specialfunctionswiki
The $q$-shifted factorial $\lt a;q \rt_n$ is given by $$\lt a;q \rt_n = \left\{ \begin{array}{ll} 1, & n=0; \displaystyle\prod_{k=0}^{n-1} (1-q^(a+m)), & n=1,2,\ldots \end{array} \right.$$
